Two-way drive for optical systems and the like

ABSTRACT

A load, such as a servomotor for the positioning (e.g. tilting) of a television camera, is operable by a control circuit provided with an input (E1) for a position signal and another input (E3) for a speed signal. The positioning signal is applied, together with a feedback signal (E2) from a position sensor, to a comparator whose positive or negative output generates an error signal of corresponding polarity and of a magnitude determined by the speed signal. A reversible load motor, coupled with the position sensor, also drives a generator to produce a reference signal of either polarity, the difference between the error signal and the reference signal producing a drive voltage of one or the other polarity for the load motor until the system is in balance.

United States Patent Hess [ 1 June 27, 1972 541 TWO-WAY DRIVE FOROPTICAL 3,122,687 2/1964 Romvari ..318/6l8 SYSTEMS AND THE LIKE2,939,066 5/1960 Crenshaw. ..318/6l8 X 3,283,231 ll 1966 Ask ..3l8 [72]Inventor: Karl Gunter Hess, Waldlaubersheim, Gerew I618 many PrimaryExaminer-Benjamin Dobeck [73] Assignee: Jos. Schneider & Co. OptischeWerke, Bad Attorney-Karl R055 Kreuznach/Rhineland, Germany [22] Filed:Oct. 12, 1970 [57] CT A load, such as a servomotor for the positioning(e.g. tilting) [211 App! sools of a television camera, is operable by acontrol circuit provided with an input (E,) for a position signal andanother input [30] Foreign Application Priority Data (E for a speedsignal. The positioning signal is applied, together with a feedbacksignal (E,) from a position sensor, to 1969 Germany 19 672'4 acomparator whose positive or negative output generates an error signalof corresponding polarity and of a magnitude ill-k8,? determined by theSpeed signal A reversible load motor, cow Field 318/618 pled with theposition sensor, also drives 'a generator to produce a reference signalof either polarity, the difference between the error signal and thereference signal producing a [56] References cued drive voltage of oneor the other polarity for the load motor UNITED STATES PATENTS until thesystem is in balance.

3,093,776 6/1963 Bird et a]. ..3l8/6l8 4 Claims, 1 Drawing Figure 1 3 Ii Am I'f'cr 0w 5 Posifion E: Com/53mm, P I I eren'hal 1 G LimiterAmplifier I T I f 7 Transmission Load My present invention relates to acontrol system for the positioning of a reversible load.

The general object of this invention is to provide means for reversiblydisplacing such a load at a constant but preferably adjustable rate,thus at a speed which is independent of the distance between the actualload position and the position sought to be obtained; this isparticularly important in cases where the load is a mechanical componentof an optical objective, a television camera or some other opticaldevice requiring smooth transition from one position to another.

This object is realized, pursuant to my invention, by the provision of areversible drive motor coupled not only with the load but also with atachometer and with a position-sensing device, the latter generating afeedback signal indicative of load position whereas the former producesa reference signal of a polarity and magnitude determined by thedirection and speed of motor rotation. A comparison circuit receivesboth the feedback signal and an externally (e.g. manually) appliedpositioning signal for deriving a bipolar error signal from thedifference thereof; a limiter stage forming part of the comparisoncircuit clips the error signal to make its magnitude independent of thevalue of the difference between the two input signals. The clipped errorsignal, whose magnitude is preferably adjustable in accordance with adesired motor speed, is impressed upon one input of a differentialcircuit (e.g. amplifies) whose other input receives the reference signalfrom the tachometer; the output of this differential circuit constitutesa driving voltage of either polarity which actuates the load motor in asense tending to reduce the error signal to zero.

By virtue of the clipping effect of the limiter stage, the motor speedin either direction is determined solely by the speed selectorregardless of the relative magnitudes of the positioning signal and ofthe feedback signal derived from the position sensor. The positioningsignal may be supplied by any conventional voltage source (e.g. apotentiometer) whose output varies in magnitude according to the spacingof a desired load position from a predetermined reference position. Theload, therefore, will approach its new position at a selected speedindependent of the distance it has to travel, this being true for eithersense of displacement.

The invention will be described in greater detail hereinafter withreference to the accompanying drawing the sole FIGURE of whichdiagrammatically illustrates a representative embodiment.

in the drawing 1 have shown a conventional comparator 1 whose two inputsE,, E receive an externally applied positioning signal and an internallygenerated feedback signal, respectively. The positioning signal, herepositive, may be larger or smaller than the feedback signal whenever thesystem is unbalanced by the operation of the voltage source connected toinput E There results, accordingly, a positive or negative error signalin the output of the comparator, this error signal being fed to anamplifier/limiter 2 having a control input E, which carries a speedsignal (here also positive) of selected magnitude. Limiter stage 2 maycomprise conventional circuitry for clipping both the positive and thenegative output voltages of comparator 1 so that, in the presence of asignificant error signal issuing from the comparator, a voltage of unitvalue :1 is generated within that stage; this unit voltage is thenselectively magnified, in steps or (preferably) continuously, by theapplied speed signal E The voltage of terminal E may be used, forexample, to set a potentiometer in the input of an operational amplifierreceiving the output of the clipping circuit, yet in a simple case sucha potentiometer could also be directly controlled by the operator withomission of terminal The output of stage 2 is a modified error signalwhose polarity is determined by the sign of the difierence between theinput voltages of comparator l and whose magnitude is manually orotherwise selected lly the o erator. This error signal is fed to oneinput of a d erenti amplifier 3 whose other input receives a referencevoltage from a tachometer 5 shown as an electric voltage or currentgenerator. Differential amplifier3 lies in the input circuit of areversible load motor 4 which is mechanically connected, via a linkage10, with generator 5 and with a transmission 6 for driving a positionsensor 7 and a load 8. Sensor 7, here shown as a'potentiometer,generates the feedback signal applied to comparator input 5,; thissensor may also include an amplifier for the feedback signal. Load 8 maycomprise, for example, a servomechanism for tilting or swinging atelevision camera within a predeter mined angular range. I

A common housing 9, indicated schematically, is shown to enclose thecomponents 1-6 of my improved two-way drive for the load 8. Components1-3 may be constituted by individually replaceable modulesinterconnected by plug-andjack couplings. Limiter stage 2 may becombined with comparator l to a single module.

The constancy (for a given setting of control input 15,) of thedisplacement rate of the load 8 in response to any voltage difference inthe input of comparator l limits the period of the instability, i.e. thetime during which the system seeks its new equilibrium, to apredetermined maximum; such a system can therefore also be used as ananalog/digital converter, e.g. for data transmission, with a fixedoperating cycle in the course of which an analog voltage applied toinput E brings about a selected operating position for load 8 togenerate (as by the selective closure of a set of contacts) the binaryequivalent of the input signal. In such a case, the feedback voltagedelivered by sensor 7 may vary in predetermined increments (rather thancontinuously) to establish the necessary number of discrete loadpositions.

I claim:

1. A control system for the positioning of a reversible load,comprising:

a reversible drive motor for said load provided with an input circuit;

a tachometer coupled with said motor for producing a reference signal ofa polarity and magnitude determined by the direction and speed of motorrotation;

position-sensing means coupled with said motor for generating a feedbacksignal indicative of load position;

a source of adjustable control voltage;

comparison means connected to receive said feedback signal together witha positioning signal and for deriving a bipolar error signal from thedifference thereof;

a limiter stage connected in the output of said comparison means formaking the magnitude of said error signal independent of the value ofsaid difference, said limiter stage having an input connected to saidsource for selectively varying the magnitude of said error signal;

and differential circuitry in said input circuit connected to receivesaid reference signal from said tachometer and a modified error signalfrom said limiter stage for deriving therefrom a driving voltage ofeither polarity to actuate said motor in a sense tending to reduce saiddifference.

2. A system as defined in claim 1 wherein the coupling between saidmotor, said tachometer and said position-sensing means includes amechanical transmission.

3. A system as defined in claim 2, further comprising a common housingfor said comparison means, differential circuitry and transmission.

4. A system as defined in claim 1 wherein said limiter stage comprisesan amplifier.

* l at k

1. A control system for the positioning of a reversible load,comprising: a reversible drive motor for said load provided with aninput circuit; a tachometer coupled with said motor for producing areference signal of a polarity and magnitude determined by the directionand speed of motor rotation; position-sensing means coupled with saidmotor for generating a feedback signal indicative of load position; asource of adjustable control voltage; comparison means connected toreceive said feedback signal together with a positioning signal and forderiving a bipolar error sigNal from the difference thereof; a limiterstage connected in the output of said comparison means for making themagnitude of said error signal independent of the value of saiddifference, said limiter stage having an input connected to said sourcefor selectively varying the magnitude of said error signal; anddifferential circuitry in said input circuit connected to receive saidreference signal from said tachometer and a modified error signal fromsaid limiter stage for deriving therefrom a driving voltage of eitherpolarity to actuate said motor in a sense tending to reduce saiddifference.
 2. A system as defined in claim 1 wherein the couplingbetween said motor, said tachometer and said position-sensing meansincludes a mechanical transmission.
 3. A system as defined in claim 2,further comprising a common housing for said comparison means,differential circuitry and transmission.
 4. A system as defined in claim1 wherein said limiter stage comprises an amplifier.